1. Field of the Invention
The present invention relates to apparatus for cooling superconductor; and, in particular, to heat insulation type apparatus for cooling superconductor.
2. Related Background Art
As a conventional apparatus for cooling a superconductor, a heat insulation type cooling apparatus for cooling a superconducting quantum interference device (SQUID) to a superconductivity transition temperature (Tc) or lower is reported in a literature (T. S. Lee et al., Rev. Sci. Instrum., 67(12), 1996). This cooling apparatus has an outer container, an inner container accommodating liquid nitrogen, and a thermal conductor for conducting the heat of liquid nitrogen. The cooling apparatus is also equipped with a position adjusting mechanism for adjusting the gap between a SQUID chip attached to the front end of the thermal conductor and a vacuum window of a cup-shaped assembly attached to the outer container.
As a result of diligent studies, the inventors have found that the above-mentioned cooling apparatus has the following problems. Namely:
1) The position adjusting mechanism and other constituent parts have a large number of components, and a bellows is necessary for allowing the cup-shaped assembly to move up and down, whereby the apparatus tends to be complicated and expensive.
2) Since the thermal conductor is elongated due to the structure of the apparatus, the efficiency of cooling the SQUID chip is not always sufficient. Also, the thermal conductor comprises a copper rod and a sapphire rod which are connected to each other. When different kinds of members are thus connected to each other, the thermal conductivity deteriorates at the junction therebetween, thus yielding a possibility that the efficiency of cooling the SQUID chip further decreases.
3) Since the structure of the apparatus is complicated, assembling and maintaining operations are cumbersome. Therefore, an improvement is desired in workability y at the time of assembling and maintenance.
In view of such circumstances, it is an object of the present invention to provide a cooling apparatus for a superconductor, which can be made at a lower cost as compared with conventional ones, is excellent in cooling performances, and is capable of improving the workability.
The inventors have further conducted studies based on the above-mentioned findings, thereby accomplishing the present invention. Namely, the apparatus for cooling a superconductor in accordance with the present invention comprises an outer container, substantially shaped like a cup, comprising a female thread portion at an inner peripheral face of an open end thereof and a window at a bottom wall thereof; an inner container, substantially shaped like a cup and disposed within the outer container, having an outer peripheral face of an open end thereof provided with a male thread portion adapted to engage the female thread portion; and a thermal conductor, disposed at a position facing the window so as to penetrate through the inner container, having one end positioned inside the inner container and the other end positioned outside the inner container, the other end having a superconductor attached thereto; wherein a space between the outer container and inner container defined by the engagement of the female thread portion and the male thread portion is vacuumed so as to form a vacuum heat-insulating layer. At the time of cooling the superconductor, a coolant for cooling the superconductor is accommodated inside the inner container.
Preferably, a lead for transmitting information obtained by the superconductor is connected to the superconductor, and the inner container is formed with an outlet for drawing out the lead therethrough.
Preferably, the apparatus further comprises an annular sealing member, disposed within the vacuum heat-insulating layer, abutting against both of the inner and outer containers at a part on the inner side of the vacuum heat-insulating layer than the engaging part of the female and male thread portions, so as to seal the vacuum heat-insulating layer.
Preferably, in this case, the apparatus further comprises a bypass member, disposed within the inner container, having one end connected to a part of the inner periphery of the inner container below the sealing member and the other end connected to a part of the inner periphery of the inner container above the sealing member, for bypassing thermal conduction from the coolant with respect to the sealing member. It is further preferred that the inner container be made of fiber-reinforced plastics.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.